The invention applies, in particular, to the display of symbologies which are referenced within a geographical frame of reference, i.e. a frame of reference which is defined with respect to the Earth, such as, for instance, the terrestrial frame of reference which defines any point on the terrestrial sphere in terms of its longitude and latitude.
On an aircraft, such symbologies are used in particular for the navigation thereof.
It is known that there are several display devices in the cockpit of an aircraft, for example electronic screens of the “Electronic Instrument System” type (EIS) or the “Control and Display System” type (CDS), which display several kinds of formats. A format is made up of several kinds of parameters (speed of the aircraft, roll angle, etc.), symbols (surrounding traffic, ground beacons, etc.) or coherent symbologies (weather images, flight plan, etc.). Usually, a display device builds the formats that it displays from data or symbols which are sent to it by the aircraft's computers. By way of illustration, generally the roll angle is transmitted by the inertial systems and the flight plan is transmitted by a flight management system.
However, if a computer provided for transmitting a parameter to a display device exhibits a malfunction, the display of that parameter, or of symbols using that parameter, is lost.